From bdeea37efc76bc22a0d2e17f66dbf2ae8ad556fc Mon Sep 17 00:00:00 2001
From: Sylvain Henry <sylvain@haskus.fr>
Date: Fri, 6 Aug 2021 18:35:06 +0200
Subject: More support for optional home-unit

This is a preliminary refactoring for #14335 (supporting plugins in
cross-compilers). In many places the home-unit must be optional because
there won't be one available in the plugin environment (we won't be
compiling anything in this environment). Hence we replace "HomeUnit"
with "Maybe HomeUnit" in a few places and we avoid the use of
"hsc_home_unit" (which is partial) in some few others.
---
 compiler/GHC/Unit/Finder.hs | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

(limited to 'compiler/GHC/Unit/Finder.hs')

diff --git a/compiler/GHC/Unit/Finder.hs b/compiler/GHC/Unit/Finder.hs
index cc16cd0dad..d4de80947b 100644
--- a/compiler/GHC/Unit/Finder.hs
+++ b/compiler/GHC/Unit/Finder.hs
@@ -134,18 +134,24 @@ findImportedModule
   :: FinderCache
   -> FinderOpts
   -> UnitState
-  -> HomeUnit
+  -> Maybe HomeUnit
   -> ModuleName
   -> PkgQual
   -> IO FindResult
-findImportedModule fc fopts units home_unit mod_name mb_pkg =
+findImportedModule fc fopts units mhome_unit mod_name mb_pkg =
   case mb_pkg of
     NoPkgQual  -> unqual_import
     ThisPkg _  -> home_import
     OtherPkg _ -> pkg_import
   where
-    home_import   = findHomeModule fc fopts home_unit mod_name
+    home_import
+      | Just home_unit <- mhome_unit
+      = findHomeModule fc fopts home_unit mod_name
+      | otherwise
+      = pure $ NoPackage (panic "findImportedModule: no home-unit")
+
     pkg_import    = findExposedPackageModule fc fopts units mod_name mb_pkg
+
     unqual_import = home_import
                     `orIfNotFound`
                     findExposedPackageModule fc fopts units mod_name NoPkgQual
@@ -154,11 +160,13 @@ findImportedModule fc fopts units home_unit mod_name mb_pkg =
 -- plugin.  This consults the same set of exposed packages as
 -- 'findImportedModule', unless @-hide-all-plugin-packages@ or
 -- @-plugin-package@ are specified.
-findPluginModule :: FinderCache -> FinderOpts -> UnitState -> HomeUnit -> ModuleName -> IO FindResult
-findPluginModule fc fopts units home_unit mod_name =
+findPluginModule :: FinderCache -> FinderOpts -> UnitState -> Maybe HomeUnit -> ModuleName -> IO FindResult
+findPluginModule fc fopts units (Just home_unit) mod_name =
   findHomeModule fc fopts home_unit mod_name
   `orIfNotFound`
   findExposedPluginPackageModule fc fopts units mod_name
+findPluginModule fc fopts units Nothing mod_name =
+  findExposedPluginPackageModule fc fopts units mod_name
 
 -- | Locate a specific 'Module'.  The purpose of this function is to
 -- create a 'ModLocation' for a given 'Module', that is to find out
@@ -166,11 +174,13 @@ findPluginModule fc fopts units home_unit mod_name =
 -- reading the interface for a module mentioned by another interface,
 -- for example (a "system import").
 
-findExactModule :: FinderCache -> FinderOpts -> UnitState -> HomeUnit -> InstalledModule -> IO InstalledFindResult
-findExactModule fc fopts unit_state home_unit mod = do
-  if isHomeInstalledModule home_unit mod
-    then findInstalledHomeModule fc fopts home_unit (moduleName mod)
-    else findPackageModule fc unit_state fopts mod
+findExactModule :: FinderCache -> FinderOpts -> UnitState -> Maybe HomeUnit -> InstalledModule -> IO InstalledFindResult
+findExactModule fc fopts unit_state mhome_unit mod = do
+  case mhome_unit of
+    Just home_unit
+      | isHomeInstalledModule home_unit mod
+      -> findInstalledHomeModule fc fopts home_unit (moduleName mod)
+    _ -> findPackageModule fc unit_state fopts mod
 
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